1. Field of Invention
This invention pertains to a system for delivering an implant to a site in a body lumen. More particularly, this invention pertains to a delivery system for a self-expandable implant such as a stent.
2. Description of the Prior Art
Stents are widely used for supporting a lumen structure in a patient""s body. For example, stents may be used to maintain patency of a coronary artery, other blood vessel or other body lumen.
Commonly, stents are commonly metal, tubular structures. Stents are passed through the body lumen in a collapsed state. At the point of an obstruction or other deployment site in the body lumen, the stent is expanded to an expanded diameter to support the lumen at the deployment site.
In certain designs, stents are open-celled tubes which are expanded by inflatable balloons at the deployment site. Other stents are so-called xe2x80x9cself-expandingxe2x80x9d stents. Self-expanding stents do not use balloons or other application of force to a collapsed stent to cause the expansion of the stent. An example of a self-expanding stent is a coil structure which is secured to a stent delivery device under tension in a collapsed state. At the deployment site, the coil is released so that the coil can expand to its enlarged diameter. Other self-expanding stents are made of so-called shape-memory metals such as nitinol. Such shape-memory stents experience a phase change at the elevated temperature of the human body. The phase change results in expansion from a collapsed state to an enlarged state.
A delivery technique for shape-memory alloy stents is to mount the collapsed stent on a distal end of a stent delivery system. Such a system would include an outer tubular member and an inner tubular member. The inner and outer tubular members are axially slideable relative to one another. The stent (in the collapsed state) is mounted surrounding the inner tubular member at its distal end. The outer tubular member (also called the outer sheath) surrounds the stent at the distal end.
Prior to advancing the stent delivery system through the body lumen, a guide wire is first passed through the body lumen to the deployment site. The inner tube of the delivery system is hollow throughout its length such that it can be advanced over the guide wire to the deployment site.
The combined structure (i.e., stent mounted on stent delivery system) is passed through the patient""s lumen until the distal end of the delivery system arrives at the deployment site within the body lumen. The deployment system may include radio-opaque markers to permit a physician to visualize positioning of the stent under fluoroscopy prior to deployment.
At the deployment site, the outer sheath is retracted to expose the stent. The exposed stent is now free to expand within the body lumen. Following expansion of the stent, the inner tube is free to pass through the stent such that the delivery system can be removed through the body lumen leaving the stent in place at the deployment site.
In prior art devices, the stent may prematurely deploy as the outer tube is retracted. Namely, with the outer tube partially retracted, the exposed portion of the stent may expand resulting in the remainder of the stent being squeezed out of the outer tube. This can result in the stent being propelled distally beyond a desired deployment site. Also, once the stent partially unsheathed, it is sometimes determined that the stent placement needs to be adjusted. With existing systems, this is difficult since the stent has a tendency to force itself out of the sheath thereby making adjustments difficult. What is needed is a system that retains the stent on the catheter even when a majority of the stent has been exposed by retraction of the sheath. What is also needed is a system that allows a stent to be re-sheathed even after a majority of the stent has been exposed by retraction of the sheath.
It is an object of the present invention to provide improved structures for self-expandable implant delivery systems such as stent delivery systems.
One aspect of the present invention relates to a method for deploying a self-expandable implant with a deployment system. The deployment system includes a sheath for holding the implant in a compressed orientation. The implant includes an implant body that extends along an axis between first and second ends. The implant also includes an interlock surface that faces in an axial direction. The interlock surface is preferably located within 5 millimeters of the first end of the implant. The method is initiated by generating relative movement between the implant and the sheath to expose the implant. As the implant is exposed, the interlock surface of the implant is engaged by a retainer to prevent the implant from prematurely exiting the sheath. After the implant has been exposed beyond the interlock surface, the interlock surface is disengaged from the retainer by self-expanding the implant. Another aspect of the present invention relates to systems for practicing the above-described method.